<!DOCTYPE html>
<html lang="en">

    <head>
        <meta charset="UTF-8">
        <meta http-equiv="X-UA-Compatible" content="IE=edge">
        <meta name="viewport" content="width=device-width, initial-scale=1.0">
        <title>Document</title>
    </head>

    <body>
        <textarea>Type something here...</textarea>
        <script>
            let textarea = document.querySelector("textarea");
            let timeout;
            textarea.addEventListener("input", () => {
                clearTimeout(timeout);
                timeout = setTimeout(() => console.log("Typed!"), 500);
            });
        </script>
    </body>

</html>